Field of Invention and Prior Art
The invention concerns a surface for sports areas, particularly tennis courts, the top layer of which consists of a setting compound formed essentially of brick dust, other mineral material, and inorganic binding agent.
Such a surface is known from the German Patent Specification No. 441 047. For the preparation of a top layer for tennis courts, according to this proposal, a composition is laid consisting of 25% fine brick dust, 20% coarser brick dust, 15% binding grit, 20% green color, 10% black lime*, 5% cement**, and 5% rock salt. Furthermore, a process is known for the stabilization of tennis courts against mechanical wear, wherein the stone mixture forming the top layer of the tennis court surface is mixed with an aqueous dispersion of water insoluble homopolymers or copolymers of vinyl compounds (see DE-OS No. 1 937 761). Furthermore, in order to minimize maintenance work and to adapt to changing weather conditions, it has been proposed to incorporate into the top layer of a playground surface granulated siliceous material of great strength, in part very hard, and having a high water-absorbing capacity, such as hydroscopic silica, kieselguhr, silica gel, vermiculite, or siliceous fireproof clay (see DE-OS No. 2 122 930). FNT *(a lump variety of hydraulic lime) ** hydraulic
These proposals have all failed in practice. So far there has been no success in producing a surface which, on the one hand, has the advantageous features of a typical barn floor with a surface of brick dust or red gravel and, on the other, possesses the resistance to wear and to winter that typical hard courts possess.
Tennis courts having a top layer of brick dust on a "dynamic layer" of brick gravel, slag particles and similar substances, are conducive to optimum playing conditions due first, to the characteristics which affect foothold and sliding, and second, to the elasticity of the entire installation. Special significance attaches to a feature allowing a predetermined degree of sliding which enables the competitor's movement energy to be absorbed by the top layer, so that a stopping action is not completely absorbed by the competitor's muscles and bones. In this way early fatigue is counteracted and the risk of injury reduced. This predetermined degree of sliding derives mainly from the fact that at a certain load individual particles of brick dust release themselves from their foundation and, behaving like balls or rollers, permit the sliding movement of the shoe on the top layer. In spite of a certain sliding characteristic the competitor must be assured of a fast start.
Considerable disadvantages accompany the good playing conditions of a tennis court having a brick dust surface as, for example, very demanding maintenance, the long retention of dampness with associated diminution of foothold, the creation of dust when the brick dust layer is insufficiently moist and, finally, low resistance to wear which leads to the known irregularities in the heavily used areas. Other disadvantages are the comparatively short life and the necessity of an annual spring service.
Some of these disadvantages do not occur with hard courts having a top layer of asphalt or concrete. However, such hard courts frequently are not satisfactory from a player's point of view because the characteristic sliding feature of the brick-dust court is missing. This increases premature fatigue and also the risk of injury; in addition, the considerable hardness and minimal elasticity of such courts leads to heavy ball wear and balls which are too fast in the case of a hard drive.